1. Field of the Invention
This invention relates to an apparatus for performing well bore tests, and more particularly to subsea well bore test apparatuses adapted to be located in a blowout preventer stack.
2. Description of the Prior Art
A removable subsea test tree is well known to those skilled in the art and is adapted to be located in a blowout preventer stack which has an upper releasable latch assembly to permit the drill pipe or other tubular string above the test tree to be released from the valve portion when the latter is in a closed condition, permitting removal of the tubular string thereabove and the temporary abandonment of the well in the event that high seas or inclement weather makes it necessary, or desirable, to do so. More specifically, one or more valves are placed in an open condition by fluid pressure pumped down a hydraulic control line extending from a drilling vessel to the three disposed in the blowout preventer stack. The hydraulic pressure control line also extends from the drilling vessel to the releasable connection. When pressure is applied through the line, the connection is released.
Typical of the prior art is U.S. Pat. No. 3,870,101, entitled "Removable Subsea Production Test Valve Assembly" which includes one or more lower ball valves which are pressure actuated to open position from the vessel or platform to permit well testing, and also an upper latch mechanism releasably secured to the valve portion of the assembly. Relieving of the pressure effects closing of one or more valves, permitting the latch mechanism to be released and removed with the upper portion of the tubing or drill pipe string to the vessel or platform. The pistons controlling the valves are pressure balanced, with the valves being adapted to permit reverse flow around them when in closed condition. A pressure actuated piston capable of forcing a lower ball valve to closed position is provided which, in so doing, cuts a wireline which may have parted above the assembly, and which would otherwise hold the ball valve open.
U.S. Pat. No. Re. 27,464 discloses a similar device which specifically incorporates plural ball valve elements and a selectively releasable latch element. U.S. Pat. No. 3,457,991 discloses a similar concept.
U.S. Pat. No. 3,071,188, discloses a remotely controlled latch mechanism which is hydraulically activated, and which may be used in conjunction with one or more valve elements in a conventional test tree apparatus. A similar latch mechanism is disclosed in U.S. Pat. No. 3,102,591.
U.S. Pat. No. 3,256,937 also discloses an apparatus and claims a method of completing a subsea well incorporating a prior art subsea test tree apparatus.